Avoiding and detecting gasoline that is leaked or spilled during the process of fueling vehicles and servicing fuel storage and handling equipment has become critically important to the operation of service stations. Left unchecked, fuel spillage could seep into the ground and contaminate groundwater. It can also volatilize and add to the presence of pollutants in the atmosphere as well as create a fire hazard. There does not appear to be any shortage of recommended approaches for dealing with these problems.
An early solution to this problem was to dig a pit or trench beneath fuel dispensers, pipes, and storage tanks and line the pits and trenches with a polymeric liner. Access ways and pipes could be placed at low points to determine whether an accumulation of fluid was present. These systems were still subject to volatilization and could also leak. Further, monitoring such a system was generally done periodically with no immediate response to a spill.
Sump boxes and other devices used for the secondary containment of piping and submersible pumps (turbines) have been in existence at least as far back as 1983. Generally, such sump boxes were placed around risers, turbines, and piping joints fixed to the turbines and elsewhere. A leak detector could be placed in such a device and wired into the service station so that the attendant would be signalled to the presence of a leak. These systems were generally nondiscriminating systems. They would sound an alarm irrespective of the liquid which would fill the box. Thus, a rise in groundwater, heavy rain, or water runoff was just as likely to sound an alarm as would leaking fuel.
U.S. Pat. Nos. 4,842,163, 4,971,225, and 5,100,024 are drawn to Gasoline Collector Pit Boxes and Submersible Unit Boxes. These patents describe containment devices that were an early response to the rising need for secondary containment strategies largely driven by regulatory schemes set forth by State and local governments. Essentially, they describe containment pans that were placed beneath dispensers or around turbines. In most embodiments, the devices had a slanted floor with a well at the low point. Spillage or leakage would thus collect in the low point. A bracket was pivotally mounted to the floor of the containment pan. A float was rigidly attached to one end of the bracket with a chain attached opposite to the float. The chain was then placed in mechanical communication with a trigger on a shear valve for shutting down the flow of fuel through the dispenser. The float rested in the low point of the containment pan. When liquid filled the low point of the pan, the float would rise, pulling on the chain and tripping the shear valve.
The combination of tripping the valve, shutting down the flow of fuel, and recognizing that this had taken place was said to result in the generation of an externally manifested signal. While other embodiments of these devices existed, they all relied upon such a mechanical action or direct physical force for the actuation of the signal and the response to that signal. For this reason and others, the devices and methods set forth in these patents left many problems unsolved. For example, the reliance on a mechanical link between the float (sensor) and the shear valve proved difficult to properly set and maintain. Furthermore, because hydrocarbons have a specific gravity that is less than that of water, it was difficult to provide a float which would work well in both hydrocarbons and water or a mixture thereof. Moreover, the only externally manifested signal provided by these devices was the recognition that a dispenser or pump was no longer operating. Clearly, there is no guarantee that such a recognition will occur in a timely manner.
Another difficulty with the systems described in these patents was that the devices used in conjunction with gasoline dispensers all had a drainage means as part of the containment pan. This drainage means drained accumulated fluids through another underground line such as the vapor recovery system common to most service stations. If one is interested in secondarily containing the system then they should also provide a system for containing the drainage means. Additionally, when the drainage means is combined with the vapor recovery system one risks returning dirty or fouled fuel and water to the fuel tank. Further still, some regulatory bodies will simply not permit such an arrangement.
Spills and leakage can also arise from heavy inadvertent contact with fuel dispensers. Typically such dispensers are large rectangular objects placed between service station driving lanes. Periodically, these dispensers will be struck by a vehicle negotiating through the lanes. Prior art methods for dealing with this problem have generally involved the placement of a shear valve between the source of the fuel (lines coming in from the storage tank) and the dispenser. When the dispenser receives a large jolt, the shear valve is tripped shutting down the flow of fuel to the dispenser. Again, there is no way to guarantee that an attendant or one responsible for maintaining the system will be alerted that this will occur. The disablement of the dispenser by mechanical means is also not as reliable or as quickly actuated as desired. An improved sensing and signalling means for such an event would add greatly to the integrity of the safety and environmental protection posture of the service station.
Those involved in formulating secondary containment strategies have not generally confronted the issue of the danger of volatilization of the fuel contained. Devices used for this purpose have generally focussed on directing spillage to a low point, a well, or other area in which accumulation of small amounts of fluids could be sensed. This allows rapid detection of fluid that is accumulating but requires some accumulation nonetheless. When this occurs, fuel can volatilize and become a much more potent fire and explosion hazard than would be the case if the fuel remained a liquid. Detection methods that do not require accumulation of fuel could help avoid this problem. Of course, where some nonhazardous fluid such as water is accumulating in the containment device one would not necessarily want to cause an alarm. Thus, an ideal system would respond immediately to the presence of fluid, would distinguish between hazardous and nonhazardous substances, and would provide an appropriate signal or response depending upon the nature of the substance and the type of response desired.
Retrofitting service stations with new electrically controlled sensors, monitors, and containment devices can be a costly and disruptive undertaking. Most service stations have concrete, cement, or asphalt accessways for the vehicles using the stations. These accessways cover the areas that contain electrical connections and many of the devices used to store fuel and get it to the dispensers. Changes requiring new electrical connections and devices could require substantial excavation, trenching, wiring and other intrusive operations. Of course, excavated areas would also have to be resurfaced. Avoiding this type of expense and trouble in the installation of new devices and sensors would also greatly benefit this area.
It will also be understood by those skilled in the art that there is a fairly heavy flow of information and many monitoring requirements associated with operating modern service stations apart from avoiding leaks and spills at the dispenser and pump. Storage tanks must also be monitored for leaks. Most modern service stations employ double wall storage tanks having an interstices between the walls. A number of different sensing technologies may be employed to monitor this interstitial space to determine whether there is leakage in the tanks. This information must be communicated when such a leak occurs.
Inventory control and other accounting and financial data is also compiled by the service station attendant. The level of the fuel in the tanks must be monitored so that inventory and supply can be controlled without interruption. As point of sale devices and microprocessors make inventory control increasingly continuous, this information multiplies. For example, it is possible to detect fuel usage, inventory, and sales by reconciling point of sale data, storage tank volume, receipts and other information. Increasingly stringent accounting control requirements require just such a reconciliation. Integrating the input from fuel storage and handling devices and other data sources could streamline this process so that most of the information required of the attendant can be obtained through one source. This would simplify service station operation and also add to the safety of such operations.
Another complication brought upon by the changing face of service station operations is the nature of the response to an alarm or signal that spillage and leakage has occurred. Fewer personnel now staff service stations on a full time basis and fewer still have technical expertise. Thus, it would be beneficial if a potential environmental or safety problem could be remotely signalled to a centralized agency capable of handling solving such a problem. For example, rather than waiting for an attendant to recognize that a large spill of gasoline has occurred, having the attendant evaluate the significance of the spill, and then alerting an agency capable of solving the problem, time and undue hazard could be saved by having a signal sent directly from the system under alarm to a response agency. Such a signal might also be sent to the fire department, a central monitoring facility, and any other interested location. Of course, it would not be helpful if every time a sensor sensed anything such a response was solicited. Thus, to be meaningful, such a system should be able to differentiate among the different sources of alarm generation and the relative severity of the source. The appropriate signal should then be sent to match the type and severity of the source of the problem.
Some of the problems noted above are addressed through system automation as set forth in application Ser. No. 08/206,291 filed on the same date as this application, entitled "Improved Site Management System for Containing Hazardous Spills and Leaks," by inventor Glen Marshall which is incorporated herein by reference. Human judgment should also not be without recourse. If an attendant receives information, from a sensor, signal, or elsewhere that continued operation of a dispenser, pump, or other fuel handling device would create a safety or environmental hazard, that attendant should be able to remotely disable the device. Response time to such information could be greatly reduced if sensor signals and controls were all centrally located.
Statistical treatment of the information generated by remote sensing means can also add to the quality of human judgment and decision making. For example, historical data concerning times and dates of spills and differentiation of the types and quantities of liquid present in containment devices can greatly contribute to the treatment of various problems. Perhaps fixtures used in association with dispensers are tightly sealed at relatively high temperatures but become loose and leaky at lower temperatures. Alternatively, containment devices may fill with fluid more readily when humid air is rapidly cooled and thereby condensed. Distinguishing occurrences such as these from mechanical failures and other mishaps could greatly aid in identifying and using the appropriate equipment for the given conditions. Accordingly, it would be beneficial if a system could be developed which avoided the problems outlined above and compiled and processed data gathered through the operation of the system.